The present invention relates to an improved resin coated sand to be used in a shell-molding process. In conventional sand molding operations, a mixture of sand coated with binder are placed in the mold, and the heat of the processing steps causes reactions to occur between the binder components to improve the pressed strength of the sand and retain the configuration of the part to be cast. After introduction of the molten metal into the cavity, the heat of the metal, during the cooling cycle is transferred to the sand-binder mixture causing the binder to be destroyed to a degree that allows the sand to be removed from the cast metal in an efficient manner.
In the automobile industry, the trend of maufacturers has led to the replacement of iron and steel casings with lighter weight metals such as aluminum, magnesium and their alloys. These castings are produced by sand-molding processes, but occur at lower temperatures than iron castings. The use of conventional binders, at these lower temperatures, have created problems in the removal of the sand particles from the castings due to the failure of the binder to be decomposed.
It has been discovered that the use of organic bromide compounds incorporated in the binder composition will alleviate the problem of particulate removal from the casting, at the lower temperatures of aluminum and magnesium castings. The removal of the sand from complicated mold structures is accomplished by agitation or flogging of the casting after the cooling cycle. Flogging is a term used to indicate a tapping or impact force applied to the castings to remove the particulate sand particles leaving a clean cast structure.
After the flogging operation the sand can be reprocessed for reuse in subsequent shell molding operations. The use of this improved binder formulation, allows this reclaimed sand to be utilized in an efficient manner.